At first glance seven spice powder may sound like a variant on Chinese five spice powder, but they couldn't be more different. Or rather, they're exactly as different as their native cuisines. Five spice, fragrant with sweet and spicy anise flavors, is the perfect compliment to meaty Chinese braises and barbecues. On the other hand, seven spice powder, or what the Japanese call shichimi togarashi, is practically built for the grilled meats, noodles, rice, and soups that so characterize Japanese cooking.
The exact ingredients and ratios may change from blender to blender, but seven spice powder is built on a foundation of chiles, dried orange peel, Sichuan peppercorns, sesame seeds (white and/or black), dried ginger, and seaweed. It likely originated in 17th century apothecaries, after chiles were introduced to Japan as a form of medicine.*
There's a long tradition of blurred lines between culinary spice blending and pharmacology. See also the tonic water in your highball; a drink that originally began as a way to make malaria-fighting quinine more palatable.
Shichimi togarashi is unusually spicy by Japanese standards, with a heat that's full and abrupt but passes quickly. Orange and seaweed provide most of the aromatic fragrance, and the combination is more arresting than you'd think. Just like a spritz of lemon brings some grilled fish to life, orange touches on the fresh, oceanic flavors of seaweed. Ginger, Sichuan pepper, and sesame seeds add layers of flavor to make this an extremely versatile blend. Just don't expect the ma la tingles of Sichuan cooking from the peppercorns; they add dimension, but are not present in high enough proportion to numb the tongue, nor are the chiles quite that incendiary.
Because it's built on so many flavors, seven spice powder transitions easily from a simple topping for rice to soup to noodles to grilled meat. It's also an increasingly popular tableside condiment in Japan, especially since it doesn't require toasting beforehand to bring out its full flavors. I'm also fond of it in marinades and sauces. Unsurprisingly, it fits right at home with Japanese pantry staples: soy sauce, sesame oil, and rice wine.
My favorite use for seven spice powder is on grilled meat. Use it as a rub to form a nice crust on quick-cooking foods like tuna or as a new addition to your burger (and mix some miso paste into the mayo!). I was going to suggest using some on chicken wings to munch during football season, but Caroline Russock beat me to the punch. So my alternative: Blend it into ground pork and grill them into patties. Wrap them in lettuce and dip them in garlic-laced soy for a spicy, juicy, intensely savory hand-held snack. With its friendliness to chile, orange, sesame, and the vegetal funk of seaweed, pork is the best protein for seven spice powder.
For uses less overtly carnivorous, look to rice and soups. Plain rice topped with seven spice makes a worthy side dish, but congee's an even better vehicle, especially with the addition of sliced scallions and sesame oil. Seven spice powder can also be used as a topping for big bowls of ramen or a mix-in to liven up miso soup.
Seven spice powder is easy to make at home, and will be especially fragrant with home-zested orange and freshly ground (dried) ginger and seaweed (look for sheets of nori, the wrapping used for sushi rolls). But as it's mostly a low-maintenance convenience spice for me I'm happy to purchase it pre-blended. Japanese groceries should carry it in abundance (make sure to buy shichimi togarashi, not ichimi togarashi, which is straight-up chile powder), but my favorite rendition comes from The Spice House.